Heat treatment of yarns

ABSTRACT

PROCESS AND APPARATUS FOR HEAT TREATING YARNS WHEREIN A YARN ENTRAINED IN A GASEOUS STREAM IS BROUGHT INTO CONTACT WITH A SURROUNDING ANNULAR STREAM OF HEATED GA AND THERAAFTER THE YARN TENSION IS ALLOWED TO FALL.

March 6, 1973 R, R. coATs ErAL 3,718,953

HEAT TREATMENT 0F YARNS Filed July l5, 1970 2 Sheets-Sheet l MM5/Vraag' March 6, 1973 R, R. CoA-rs ET AL 3,713,953

HEAT TREATMENT OF YARNS Filed July 13, 1970 2 Sheets-Sheet l United States Patent O U.S. Cl. 28-72.1 11 Claims ABSTRACT OF THE DISCLOSURE Process and apparatus for heat treating yarns wherein a yarn entrained in a gaseous stream is brought into contact ywith a surrounding annular stream of heated gas and thereafter the yarn tension is allowed to fall.

This invention relates to the heat treatment of yarns and strands and in particular to the treatment of yarns or strands of thermoplastic polymeric material with a heated gaseous fluid.

In the production of artificial or synthetic thermoplastic continuous tilamentary yarns they are subjected to a drawing or stretching process under tension, following which it may be required to relax the yarn partially or completely either to produce the desired physical properties, such as a reduced shrinkage propensity in the processed yarn or to produce some other effect, such as bull-ting or crimping of the filaments comprising the yarn when these have an inherent tendency to retract into a crimped form under low tension, optionally assisted by heat.

Hitherto such relaxation has been carried out either by a batch process, wherein the yarn is temporarily collected in some form of package which allows a degree of contraction to take place or by transporting the running yarn into a heated zone by means of a stream of gas. These methods do not always produce a satisfactory product and it is one object of this invention to provide an improved method of heat relaxation of yarns wherein some bulk may be introduced into the relaxed yarn.

According to the present invention we provide a process for the heat treatment of yarns or strands wherein a yarn or strand is entrained in a gaseous stream and is carried therewith substantially axially into contact with an annular stream of heated gaseous fluid the two streams and the yarn or strand thereafter intermingling 'with a reduction in fluid pressure and at least partial relaxation Of the yarn.

A process according to the invention may be used for heat treatment of any kind of textile yarn, as for example continuous filament or staple fibre yarns composed of a synthetic thermoplastic polymer, or a staple fibre yarn composed of natural fibres or mixtures of synthetic and natural fibres. The invention is particularly suitable for treating yarns composed of or containing thermoplastic fibres or filaments by reason of the uniformity of heat treatment which may be achieved but it may also be used for the surface treatment of yarns, particularly natural libre yarns which require the removal of protruding libre ends by charring by adjustment of the temperature of the heated gaseous fluid.

One type of yarn which may be very efficiently heat treated in a process according to this invention is one composed of thermoplastic continuous conjugate filaments or of conjugate filaments in staple libre form. Such filaments, which are composed of two or more components arranged in contiguous fashion either side-by-side or as an eccentric sheath and core along the length of each filament, Will have an inherent tendency to contact into crimped form on heating if,I as is usual, the com ponente have a different shrinkage propensity. 1

Other types of yarn, which have an inherent retraction tendency and which may be advantageously treated in a process according to this invention, are those in which the retraction tendency is produced by asymmetric heating or cooling of the filaments comprising the yarn during their manufacture or which are composed of a mixture of high and low shrinkage filaments or fibres.

According to another aspect of this invention 'we provide apparatus for the heat treatment of yarns or strands comprising means for entraining a yarn or strand in a gaseous stream, a yarn or strand passageway connected to the outlet of said entrainment means and an annular passageway surrounding the yarn or strand passageway for at least part of its length.

Structures of higher denier than textile yarns, herein referred to as strands, may also be effectively treated according to this invention. One such strand is one composed of conjugate `filaments of thermoplastic material an outer component of which is of lower melting or softening point than the other or others. Filaments 0f this kind have the property of bonding to other filaments at points of contact if treated for a sufficient length of time at a temperature between the melting or softening point of the most easily fusible component and that of the next most fusible component. The degree of bonding of a strand composed of filaments of the foregoing kind when treated according to this invention may be varied by control of operating variables such as the temperature of the heated fluid and the relative speeds of the two gaseous streams. If required further bonding may be effected in means following apparatus according to the invention, as for example an oven through which the relaxed strand may be transported under gravity or on a moving belt.

Air is the most convenient gas for entraining a yarn or strand in the present invention and a simple air ejector, which may have any one of several forms, may be used. One such form comprises an entry passageway of narrow bore into which a yarn or strand is drawn by the suction developed therein by entry into the passageway of air under pressure downstream of the point of entry of the yarn or strand said air proceeding through the passageway in a generally downstream direction carrying the yarn or strand with it. An air pressure is used such as to provide the required tension to draw the material from a supply means into the entry passageway and forward it to the heat treatment zone.

In another form of ejector an entry tube or passageway which is quite short is surrounded at its lower end by the open end of a slightly larger tube. The junction of the two tubes is enclosed in a chamber to which air under pressure is supplied. The air enters the larger tube through the space between the two tubes and in passing through the larger tube induces a reduced pressure in the entry passageway which draws a yarn or strand thereinto tensioning and forwarding it through the larger tube t0 the heat treatment zone.

Air or other gas supplied to the ejector is preferably unheated but a gas at a temperature above ambient may also be used and for some treatments, as for example treatment to produce a self-bonded product, a heated supply gas may be advantageous. When an inherently retractable material is to be treated and a heated supply gas used, the temperature of the supply gas should not be so high that the retraction properties are impaired by heat treatment while under some tension in the ejector.

Whatever form of ejector is used it must provide suicient tension in the material to draw it from the source at a sufficiently high speed but without the need for an air fiow so great that the intermingling of ejector and treatment gases and treatment in the hot zone is adversely affected. It is also preferred that the air flow is insufficient to cause entanglement or looping of the filaments cornprising a filamentary yarn or strand. However as continuous dilamentary textile yarns to be treated have only a small degree of twist or none at all the air stream has an opening effect on the yarn which allows the laments to disengage from each other to some extent, an effect which may enhance the effect of heat treatment as the yarn passes through the heated fluid. Staple fibre yarns usually have a higher degree of twist to give the yarn the desired tensile strength which twist opposes any opening effect of the air stream. As staple fibre yarns are usually heat treated to remove or reduce the number of projecting fibre ends such lack of opening is beneficial.

Continuous filament yarns treated according to this invention, in particular yarns which have an inherent retraction effect, may have a unique resistance to debulking when the treated yarn is subjected to tension. This property' is believed to be due to the presence of some overtreated filament portions in the yarn which are substantially straight and are shortened, together with those which have curled into a crimped configuration, the former resisting applied tension and the latter producing bulk. This tension resistance is carried into fabrics woven, knitted or otherwise produced from treated yarns and imparts highly attractive aesthetics to the fabrics.

It has been proposed to produce tension resistant yarns by a complex method which is not easy to control and which involves feeding two or more yarns at very different rates through a zone of turbulence to produce a yarn comprising a load-bearing core of filaments of one yarn surrounded by entangled loops of the filaments fed in at the higher rate. It is an advantage of a process according to the present invention that tension resistant yarns may be simply produced from a single starting yarn.

In treating yarns or strands which are inherently retractable or are of the foregoing bondable kind it is necessary to maintain the yarn or strand in a low or substantially tensionless state during its passage through the heated fiuid and for a period afterwards while it is still hot. It is preferably also to allow a treated textile yarn to cool before collection and this may be achieved by allowing a sufficient distance between the mixing point of the fluids and any means for collecting the treated yarn together with a tension barrier, such as a roll/nip roll combination operating at a peripheral speed less than the yarn speed through the heated Huid, situated before the collection means. At higher speeds the required cooling distance may become impracticably large and we have found that a device somewhat similar to an air ejector used for entrainment of a yarn in the gaseous stream may be used instead. If such a device is placed sOme distance from the fluid mixing zone and is operated so that the air fiow is counter to the direction of yarn movement, the device will act both as a cooling means and as a tension barrier and as such may be used in addition to a roll/nip roll combination. If the degree of relaxation in and subsequent to the fluid mixing zone is to be controlled it is preferred to use a roll/nip roll in addition to the air jet tension barrier as control is thereby rendered easier. Alternatively or additionally a cooler/tension barrier of the foregoing type may be positioned after the roll/nip roll combination.

The effect of a treatment according to the invention may be varied to some extent by control of the conditions of treatment, as for example the yarn speed, the rates of flow of entrainment and heated fiuids and the temperature of the heated fiuid. It is important in the treatment of textile yarns to adjust the roll/ nip roll peripheral speed so that there is formed between the treatment device and the nip roll a loop or arch of adequate cooling length. For example, for a yarn composed of conjugate filaments comprising two ethylene terephthalate polymers of different intrinsic Viscosity, in which it is intended to produce bulk by the treatment, heated fluid temperatures in the range Z50-400 C. at yarn feed speeds of 450-600 metres per minute are suitable. Low entrainer gas flows of the order or" 0.25 m.3 per hour (expressed at S.T.P.) may be used together with somewhat higher heated fiuid flows.

The invention will now be further illustrated by reference to the accompanying drawings wherein:

FIG. 1 is a diagrammatic representation of apparatus for carrying out a process according to the invention.

FIG. 2 is a cross sectional view of one form of entrainment device and PIG. 3 is a cross-sectional View of a treatment device.

In these drawings like numerals indicate like parts and the devices illustrated may be used equally for treating a textile yarn or a strand. In the following description for the sake of simplicity treatment of a yarn only is referred to.

Referring now to FIG. 1 a yarn entrainment device 2 is joined to a treatment device 4 by a yarn passageway 3. The forward end of passageway 3 is surrounded by an annular passageway 5 the exit of which is just before the exit of passageway 3. A pigtail guide 10 is positioned below the entrainment and treatment devices 2 and 4 and just before the nip of a pair of rolls 6` and 7. Roll 6 is a chrome plated steel roll and roll 7 is a rubber covered nip roll pressed against the surface of roll 6. A cooling device 20 of the type described previously is located after the nip rolls 6 and 7.

In operation a yarn 1 from a supply of yarn (not shown) is drawn into the device 2 (shown in more detail in FIG. 2) by the passage therethrough of air at ambient temperature entering at 8. The air stream carries the yarn 1 through passageway 3 to the outlet thereof and shortly thereafter into contact with an annular stream of heated air supplied to the passage S at 9. On leaving the exits of passageways 3 and 5 air pressure falls and so does the tension in the yarn. This drop in tension together with the action of the heated air cause the required effect on the yarn, as for example retraction if it is an inherently retractable yarn, after which the yarn cools somewhat and passes via the guide through the nip of rolls 6/7 and through the cooling device 20 and is then collected by means not shown. The peripheral speed of rolls 6/7 is preferably somewhat lower than the speed of the yarn issuing from passageway 3 and these rolls serve to prevent winding tension passing back -to the relaxation zone which follows the exits of passageways 3/5.

An entrainment device 2 is shown in more detail in FIG. 2 wherein a body 11 has a longitudinal bore into which are fitted two tubes 12 and 3. Tube 12 comprises the yarn entry and is adjustably inserted in the bore by means of a fitting 13 which screws into an enlargement of the upper end of the bore. Tube 12 is of slightly smaller outside diameter (in a typical example smaller by 0.025 mm.) than the internal diameter of tube 3 into the upper end of which the lower end of tube 12 is inserted a small distance, which distance may be varied by means of fitting 13. The tubes 12 and 3 are substantially coaxial and around the point of intersection of their ends the bore is enlarged to provide a reservoir of compressed gas which is supplied from a flexible tube (not shown) connected to a metal inlet tube 14 screwed into body 11. Tube 3 may be continuous to its outlet from the treatment device or the two devices may be separable by use of a suitable coupling in the portion of tube 3 between the entrainment and treatment devices 2 and 4.

As illustrated in FIG. 3 a treatment device comprises a yarn passageway 3 inserted in the bore of a body 15 which has an integral inlet 16 for heated ffuid at about the midpoint, the inlet orifice of which opens into the bore at a point where it is enlarged to form an annular passageway 5 surrounding tube 3. The enlargement 5 continues to the exit from body 15 at or near which point the tube 3 also terminates. Optionally the outer wall of the body towards the open end may be tapered as shown at 17 as this reduces turbulence effects at the exit.

In operation compressed gas from inlet 14 in passing between tubes 12 and 3 proceeds down tube 3 giving rise to a suction in tube 12 which draws a yarn 1 thereinto. The flow of gas carries yarn 1 to the outlet of tube 3 where it meets an annular flow of heated fiuid issuing from passageway 5. In practice a cone fo cooler gas is formed at the mouth of tube 3 surrounded by an annulus of hotter gas, the gas flows thereafter mixing and falling first to a uniform temperature (at about 20 mm. from the mouth of tube 3 in a typical example) and then to progressively lower temperatures.

Attention is drawn to FIG. 1 in which the inner and outer cones are portrayed in dashed lines.

A surprising feature of this invention is high stability of the loop of relaxing yarn which is formed and its insensitiveness to accidental disturbance. In fact the running yarn in the loop may be appreciably and repeatedly displaced by manual contact with no apparent effect on the treatment process.

In some cases it may be beneficial to increase the length of time during which a yarn is in contact with the high temperature uid and this may be readily accomplished by extending the exit of passageway 5 beyond the exit of passageway 3. This modification may allow either a lower temperature to be used for the same yarn speed or a higher speed for the same temperature. In this case fluid fiows are adjusted so that the yarn continues to move axially along the extended passageway beyond the exit from passageway 3. Modification of the treatment device in this way may be particularly beneficial when a bondable strand is treated.

Intermittent variation in the effect of heat treatment may be deliberately introduced in a process according to this invention by momentarily displacing or impeding movement of the running yarn. One effective method of doing this is to momentarily trap the yarn just before entering the entrainment device between a rapidly vibrating wire and a stationary rubber surface.

The examples which follow illustrate the invention and the manner in which it may be performed. The properties of the products, specific volume and retraction under load are measured as described below. Specific volume is a meature of the bulkiness of a specimen and is usefully measured at low and high tensions, the low load being sufficient to enable the test to be carried out but insufficient to cause any significant debulking of the specimen and the high tension being of the order or tension met within for example weaving. Retraction under load is a measure of the alteration in length of a specimen due only to crimp formation.

Specific Volume: This property is measured by filling a bobbin of known fillable volume with the specimen yarn at a fixed tension and weighing the amount of yarn required to fill the available space. Specific volume is then calculated in cm3 per gram. The low tension measurement is carried out at a tension of 5 g. for yarns of textile denier, that is about 25 to 300 denier. The high tension measurement is carried out at a tension of 50 g.

Retraction under load: A hank of the specimen filament or yarn, made by taking ten 1.1 metre Wraps on a wrap wheel, is suspended for two minutes in boiling water under a load of 0.003 g. per denier and the shrunk length (L1) measured first under this same load of 0.003 g. per denier then under a load of 0.3 g. per denier (L2) which is suliicient to decrimp the specimen. The retraction under load is then expressed as Lz-Lr EXAMPLE 1 A conjugate multiflament oriented yarn of 150 denier containing 72 filaments composed of equal proportions of two ethylene terephthalate polymers of 0.47 and 0.67 intrinsic viscosity (measured at 25 C. in solution in 0- chlorophenol) arranged in side-byf-side fashion is treated in apparatus as illustrated in the drawings. The entrainment device is supplied with compressed air at a gauge pressure of 5.6 kg. per cm2 which draws the yarn through the device and forwards it to the treatment device at a speed of 460 rn. per minute. The amount of air consumed by the entrainment device under these conditions is 0.25 m.3/hour measured at S.T.P. (15 C. and 760 mm. Hg). Heated compressed air at a temperature (measured at the surface of passageway 5) of 300 C. is supplied to the treatment device and flows therethrough at a rate of 1.1 m.3/hour (again at S.T.P.). The yarn leaving the treatment device forms a loop of total length 115 cm., of which 50 cm. is the substantially straight portion immediately following the exits from the treatment device, before reaching the nip roll combination, which has a peripheral speed of 635 m. per minute, after which it is wound into a package at a tension of 6 g. This yarn can be woven into attractive fabrics having useful bulk and good handle.

EXAMPLE 2 A 13,000 denier strand of conjugate filaments consisting of equal proportions of linear polyethylene and isotactic polypropylene in side-by-side relationship is passed through an entrainment and treatment device as illustrated in the drawings with the exception that devices are arranged coaxially. Compressed air at 20 C. is supplied to the entrainment device, passing through it at m. per minute thereby drawing in the strand and forwarding it at 60 m. per minute to the treatment device the outer annular tube of which is supplied with air heated to 220 C. having a velocity through the tube of 105 m. per minute also. The end of the outer wall of the annular treatment tube extends a short distance beyond the end of the inner strand passageway and the treated strand emerges at 23 m. per minute.

The emergent strand is bulky and very coherent due to bonding of fibre intersections and is also well stabilised against the effect of heat up to temperatures of about C.

EXAMPLE ,3

A conjugate multiflament oriented polyester yarn as used in Example 1 is treated as in that example with the exception that the temperature of the treatment air is 205 C. The product is a bulky yarn having a specific volume of 3.66 and 1.28 cm.3 per g. under low and high tension respectively, and a retraction under load of 8.3%. For comparison a 150 denier oriented yarn composed of 72 filaments of polyethylene terephthalate of intrinsic viscosity 0.67 has a specific volume of 0.9 om.3 per g. at high tension which is not signicantly altered at low tension.

EXAMPLE 4 A conjugate multiflament oriented polyester yarn as used in Example 1 is treated as in that example with the exception that the feed speed to the treatment device is 825 m. per min., the treatment temperature is 400 C. and the nip roll peripheral speed is 655 m. per min. The product is a bulky yarn having a specific volume of 3.50 and 1.52 cm.3 per g. under high and low tension respectively.

EXAMPLE 5 A conjugate multiflament oriented yarn of denier containing 40 filaments composed of equal proportions of two polyamide components (a) polyhexamethylene adipamide and (b) a terpolymer derived from hexamethylene diammonium adipate, epsilon caprolactam and hexameth ylene diammonium isophthalate in the ratios 80:10:10 by weight the components being arranged in eccentric sheath/core arrangement with component (a) as the core, is treated in apparatus as used in the preceding examples using a feed speed of 370 m. per min. a treatment temperature of 300 C., a treatment air ow of 0.75 m.3 per hour and a nip roll peripheral speed of 280 m. per min. conditions otherwise being as in Example 1. The product was a bulky yarn having a specific volume of 1.6 crn.3 per g.

What is claimed is:

1. A process for the heat treatment of yarns or strands comprising: entraining the yarn or strand in a moving gaseous stream and passing the yarn therewith in an axial direction, forming an annular stream of heated gaseous fluid flowing in the same direction as the moving yarn, moving the yarn and the entraining gas stream axially into contact with the annular stream, at least partially relaxing the yarn or strand by intermingling the two streams and the yarn or strand to elTect a reduction in fluid pressure, continuing to move the yarn or strand axially under low tension while still hot, cooling the yarn or strand, and collecting the yarn or strand.

2. A process according to claim 1 wherein the entraining stream is an unheated gaseous stream.

3. A process according to claim 1 wherein the gas flows are insuicient to cause entanglement or looping of filaments.

4. A process according to claim 1 wherein the yarn or strand comprises a material selected from the group consisting of continuous filaments, and staple libres of a synthetic thermo-plastic polymer, natural staple fibres and mixtures of synthetic and natural fibres.

5. A process according to claim 4 wherein the yarn or strand comprises conjugate filaments in continuous or staple form.

6. A process according to claim 4 wherein the yarn or 8 strand comprises conjugate filaments having two polyester components diifering in intrinsic viscosity.

7. A process according to claim 4 wherein a yarn or strand comprises conjugate bicomponent filaments an outer component of which is of lower melting or softening point.

8. A process according to claim 1 wherein air is the entrainment fluid.

9. A process according to claim 8 wherein air is the heated gaseous uid.

10. A process according to claim 1 including causing the treated yarn to follow a looped or arched path and cooling the yarn in said path.

11. A process according to claim 1 including cooling the treated yarn by passing it through a countercurrent iiow of cooling gas.

References Cited UNITED STATES PATENTS 3,262,181 7/1966 Hawkins et al. 22S-72.11 3,548,469 12/1970 Scherzberg et al. 28-72.11 3,558,760 1/1971 Olson 2li- 72.17 2,302,790 11/ 1942 Modiglian 28-1.3 X

FOREIGN PATENTS 529,253 9/ 1921 France 28-63 LOUIS K. R-IMRODT, Primary Examiner U.S. Cl. X.R. 28-63, 72.12 

